It is well known to provide a power supply arrangement which includes a power supply, such as a DC converter or switch mode power supply (SMPS), which is responsive to an input voltage to produce a controlled output voltage for example for powering electronic circuits. Such a power supply typically includes a control circuit which compares a fraction of the output voltage with a reference voltage, the result of the comparison being used in a control loop to control or regulate the output voltage.
In such a power supply arrangement the control circuit includes active components, such as a comparator and a source of the reference voltage, a supply voltage for which is derived from the input voltage. Alternatively, it may be desirable for the control circuit to be powered by the output voltage of the power supply.
For example, the related application describes a power supply controller including a power supply for a control unit of the power supply controller which conveniently can comprise an ASIC (application-specific IC or integrated circuit). The power supply includes its own control unit, parts of which are conveniently incorporated into the ASIC. The ASIC is powered by the output voltage of the power supply, so that the control unit of the power supply is powered by the output voltage of the power supply. In this case for example the output voltage of the power supply may be 3.3 volts and the input voltage may be 48 volts, so that the input voltage is much greater than the output voltage.
On start-up of such a power supply arrangement, when the input voltage is initially connected so that it rises from zero volts to its normal value of for example 48 volts, it is possible for the power supply to fail to start up, or to start up in a manner that can produce an incorrect output voltage. These undesirable results can arise in particular as a result of indefinite or undefined characteristics of a reference voltage source of the control unit at very small values of the output voltage of the power supply powering these components.
Accordingly, there is a need to provide a power supply arrangement in which such undesirable results are avoided.